Rotary shock absorbing sub unit



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United States Patent O asoman RGTARY SHCK ABSRBING- SUB UNIT .lohn B.Coulter, Jr., Fort Worth, Tex.,. 'assignor`to Chicago Pneumatic ToolCompany, New Yon-k, N.Y., a corporation ot New Jersey Filed Feb. 2,1965. Ser. No. 429,797

` 4 Claims. .(Cl. 64;;23)

This invention is directed toa shock absorbing sub unit for use in thedrill string Aof, a rot-aryI earth-boring drill. The conventional rotaryearthsboring drill comprises a string of drill pipe at thebottomof whichis carried a rotary bit. Rotation of thestringis transmitted to the bit.As the latter rotates, cutters at lthe bottom thereof bore down into theearth. As ,the depth ofthe hole increases,l

lengths of pipe are added as needto the drill string. During drillingoperations, drilling tluid is fed through the drill string and bit tothebottom o-f the hole to aid inthe progress of the work. As the bit isrotated and the cutters roll over the bottom of the hole, verticalvibrations or bounce develop, and are transmitted-back through the drillbit to the `drill string. Vibrations are also produced by other causes,-suchas impacts to the `drill string occurring when the drill isbeinglowered into a hole. The thrust or roughness of the vibrationsvaries according to the earth formations encountered. They are'particularly strong in rough drilling operations, such as where`fractured har-d formations and alternate strata of hard and softIformations are encountered. Broken bit teeth, damaged cutter bearings,twisting and failure of sections of the drill string, jammed or -frozenjoints, and damage to surface equipment, as well as other damage oftenresult from vibrations developing during drilling operations. Thepossibility of 4dam-age from vibrations to the drill bit and drillstring becomes greater as the depth of the hole and the consequentweight of the drill string increases. Increased rotary speed coupledwith undesirable vibrations and a long drill string often result inundesirable twisting and breakage of the drill string. To avoid thepossibility of costly damages in rough drilling operations, the-speed ofpenetration and the weight load on the bit are limited by the operator.This undesirable precaution slows the dri-lling operation, and oftenresults in a hole of relatively shorter depth than mig-ht otherwise beobtained.

The general object of this invention is to provide in a rotaryearth-boring Adrill practical and economical means for effectivelyabsorbing vibrations and shocks produced duringearth-boring operations,so as to prevent them from damaging the drilling apparatus. This willsave not only the costly expense of repairs and replacement of drillingequipment that might otherwise occur, but it will also enable relativelylonger strings to be used, deeper holes to be drilled, and increasedrotary speed to be irnprarted to the drill stri-ng. The presentinvention, whereby these benecial results are obtained and wherebyundesirable vibration problems associated with earth-boring drillingoperations are substantially solved, represents a desirable technicaladvance in this particular art.

A further and more specic object of this invention is to provide in thedrill string of a rotary earth-boring drill a sub unit for accomplishingthis gener-al object. It functions to not only materially absorb anddampen the shocks and vibrations produced during drilling operations,but also functions to transmit the torque of the drill string to thedrill bit. This sub unit is preferably located in the drill string justabove the drill bit.

A4 feature of the sub unit is a shock assembly comprising a long stackof resilient shock absorbing elements which effectively preventsvibrations occurring during drilling operations from harmfully atectingthe drill string. The shock absorbing elements are so arranged in thesub unit that they are protected from attack by settima Patented Jan.31, 1967 2i drillingnuidnand `destructive drill dust. Another advantageofthe desirable arrangement'ot the' shock absorbing elements-is thatthey are separate from one another and maybe individually replaced whenw-orn.

. A feature of the shock absorbing elements lies in their particularconfiguration and in the arrangement of each element between la pair ofmetal surfaces, whereby compressive action upon'the elements causesthem-to become compressed axially and expanded radiallyv to the fullextent of their ow characteristics.l

A still furtherfeature of the sub unit is a squared drive shank `whichfunctions to transmit rotary torque'from a driving ,mandrel coupled tothe drill string directly toan inner mandrelcarrying the drill bitwithout any of such torque vpassing through the shock assembly.

In the `accompanying drawings:

FIG. 1 is an elevational View of a bodyin g theinvention; v

FIG. 2 is an enlarged view of a section taken on line 2--2 of FIG. l;

FIG. 3 is a detail .view,'partly in section, of one of the rotary subunit em` n shock absorbing rings;

FIG..4 is a detail View, partly in section, of one ot the metal spacerrings;V v

FIG. S is a` fragmentary view similar to FIG. l but showing the sub unitin fully loaded or closed condition;

FIG. 6 is a fragmentary view of the sub unit in a partially loadedcondition between that of FIGS. l and 5; and

FIGS. 7,-8 and 9 are respectively enlarged views of correspondingportions of FIGS. l, Sand '6 for purposes of comparison.

Reference is now directed to the several gures of the drawings whereinthere is disclosed a shock absorbing sub unit generally designated 10.It is adapted to be axially aligned and coupled at one end with a string11 of drill pipe in a rotary earth-boring drill. It is adapted to becoupled at its opposite end with a rock bit 12. Rotation of the drillstring 11 is transmitted through the shock absorbing sub unit 10 to thebit to cause conventional roller cone cutters (not shown), mounted tothe bottom of the bit to bore into the earth. Vertical vibrations orbounce developed by impact of the bit and ro tation of the cone cuttersduring drilling operations are transmitted upwardly through the bit tothe sub unit.

. Incorporated in the sub unit is a shock absorbing means or assembly 13which materially dampens and absorbs these vibrations so as to preventthem from being transmitted from the sub unit upwardly to the string ofdrill pipe 11. An axial passage 14 through the sub unit serves to allowow of the usual drilling uid from the drill string to the drill bit.This fluid flows through conventional passages in thelatterto the bottomof the hole where it aids in the' progress of the drilling operation.

The sub unit includes an outer cylindrical open-ended driving mandrel15.` The latter is adapted to be connected by means of a coupling 16 tothe drill string 11 for rotation as a unit with'the latter. The coupling16 has at one end a screw pin 17 adapted to be screwed into aninternally threaded axial recess or box 18 of the drill string 11; andit has at its opposite end a similar screw means of a polygonal orsquared shank portion 25 which is engaged in a complementary socket 26formed in the bottom end of the outer mandrel. The shank portion 25 hasaxial sliding movement in the socket 26. An annular shoulder 27 at thelower end of the squared shank is cooperable with an overhead end wall28 of the socket 26 to limit the extent of relative upward movement ofthe shank portion.

The extent of downward and outward movement of the shank portionrelative to the socket is Curbed by an open-ended cylindrical safetyheader 29 attached to an elongated reduced cylindrical stem 31 at theupper end of the inner mandrel. The attachment of the safety header 29and stem 31 is defined by a uid tight threaded connection at 32 in whichthe lower end of the safety header is screwed over the lupper end of thestem. A radially extending plug 33, here of nylon plastic, in the stem31 may be employed to strengthen the tightness of the connection 32. Ashoulder 34 defined by the bottom end wall of the safety header iscooperable with a stop defined by an annular shoulder 35 of a radialinternal flange 36 of the -outer mandrel to limit the extent of downwardmovement of the inner mandrel relative to the outer mandrel. Below thethreaded connection 32, the stem 31 has an axial slidable relation withthe annular inner diameter wall of the iiange 36. Because of thethreaded connection 3.2, the safety header 29 is slidable axially as aunit with the inner mandrel relative to the outer mandrel. In thismovement, the safety header bears against a surrounding inner wall area38 of the outer mandrel 15. The safety header further serves to preventthe inner mandrel 22 from dropping by force of its own weight free ofthe outer mandrel and 'becoming lost in the hole durin-g the time thedrill string is being raised to the surface or lowered into the drillhole.

The shock absorbing means or assembly 13 is arranged in coaxial relationto and `between the inner and outer m'andrels so as to cushion axialthrusts created by opposed movements of one mandrel relative to theother. The shock absorbing means comprises an elongated stack of`resilient shock absorbing rings 39, each separated from the other bymeans of a spacer ring 41. Here, the rings 39 are `formed of resilientcompressible material, such as rubber. The spacers are of rigidconstruction, and are here formed of steel. The assembly 13 is `confinedin an annular channel or space 42 defined between the inner and outermandrels by an enlargement of the interior of the outer mandrel. Theassembly 13 is disposed in surrounding relation to the stern 31 of theinner mandrel and has relative slidable movement therealong. Theuppermost resilient ring 39 of the assembly abuts against an annularshoulder 43 defined yby the underside of the internal liange 36. Thelowermost resilient ring 39 of the assembly rests upon an annularshoulder 44 defined by a cylindrical enlargement 4S at the base of thestem 31 of the inner mandrel. This enlargement is located between thestem 31 and the squared shank 25 of the inner mandrel; and it is ofreduced diameter relative to the squared shank. The cylindricalenlargement 45 extends at all times in part within the annular channel42; and has axial slidable movement therein in the manner of a piston orram relative to the shock assembly 13.

It can be seen Iduring drilling operations, that as the drill bit 12`bores into and moves over hard irregular rock formations at theKbott-om of a drill hole, the resulting vibrations created will causethe inner Amandrel 22 at tached to the bit to move -up and down relativeto the outer mandrel 15. The constant weight of the drill string 11,acting through the outer mandrel and through the flange 36 upon theshock assembly 13, biases the inner mandrel downward. As the innermandrel is caused, as a result of vibrations developed by the ybit atthe bottom of the hole, to move upwardly, it acts through itscylindrical piston portion 45 to exert an upwardly compressive forceupon the shock assembly 13 to slide the elements 4 39 and 41 thereoftoward each other. The energy exerted by the upward movement or thrustsof the inner mandrel upon the shock assembly is substantially spent incompressive action upon the latter and is thereby materially absorbedand dampened. As a consequence, the upward thrusts of the inner mandrelare prevented from passing through the outer mandrel 15 upwardly to thedrill string.

The steel spacer rings 41 have a close slidable relation to the opposedwall areas of the channel 42 and the stem 31 so that they are caused atall times when pressured upwardly or downwardly to slide at right anglesAto the walls o-f the channel 42 and stem 31, and thus `will not turnaskew. These spacer rings are highly polished so as to permit them tomove in the channel 42 with a minimum of friction. The peripheral edges46 of the spacer rin-gs are rounded, as indicated in FIG. 4, to preventscoring of the walls of the channel.

To obtain desirable flow deformation characteristics in the resilientrings 39 when the latter are under compression, these rings are formedso as to provide some free space between them and the side walls of thechannel. Here, the rings 39 are hexagonal in cross section, whereby, as`besty shown in FIG. 7, `free spaces 47 are provided adjacent thecorners of the rings. This configuration of the rings 39 is of furtheradvantage in that it provides opposed broad upper and lower fiatsurfaces 48 centered upon opposed flat faces 50 of the spacer rings 41,whereby a desirable broad support is provided for each resilient ring39. This hexagonal configuration of the resilient rings 319 is of stillfurther advantage in that opposed side corners 49 thereof are at alltimes in contact with the opposed walls of the channel 42 and stem 31whereby undesirable side to side shifting of the rings 39 is avoided.The separable nature of the rings 39 from one another is of furtheradvantage in that the individual rings may be discarded Iwhen worn, andreplaced.

During drilling operations, drilling fluid is fed down the string 11 ofdrill pipe through the flow passage 14 of the sub unit 10 to the drillbit 12 from where it flows through the usual ports in the bit to thebottom of the hole. So as to prevent this fluid from by-passing the flowpassage 14 and leaking around the safety header 29 to the shock assembly13, a nipple or wash pipe 51 is provided. This pipe has an axial fluidtight threaded connection 52 at its upper end in the pin 19 of the topcoupling 16. At its lower end the wash pipe has a slide t in the upperportion of the safety header 29. Leakage between the wash pipe and thesafety header is sealed out by means of packing 53, best seen in FIG. 5,seated around the wash pipe in a counterbore of the safety header. Agland nut 56, screwed into the countenbore, holds the packing influid-tight relation to the wash pipe. As the inner mandrel 22 is causedto move up and down relative to the louter mandrel 15 from vibrationsimparted to it, the safety header 29 is carried with it and slidesrelative to the wash pipe 51. A further seal defined by an O-ring 55 isprovided as a precaution in the periphery of the safety header to sealthe safety header Huid-tight relative to the inner wall area 38 of theouter mandrel.

It is to be noted that the shock assembly 13 is not subject to rotarytorque transmitted from the outer mandrel to the inner mandrel sincethis torque is transmitted directly to the inner mandrel through thesquared drive connection 25, 26. Accordingly, the shock assembly is notsubjected to twisting and shearing forces to which it might otherwise besubjected were the torque of the outer mandrel transmitted 4through theshock assembly to the inner mandrel.

It is understood that, as the load on the shock assembly progressivelyincreases, the resilient elements 39 of the shock assembly will beprogressively compressed from a condition as in FIGS. 1 and 7 whereinthey are under no load, as at the start of operations, until they havereached a solid 0r fully closed condition as shown in FIGS. 5 and 8wherein they are under maximum load. Up to the time the shock assemblyreaches the fully closed or loaded condition of FIGS. and 8, it willprovide shock absorbing characteristics. The load upon the shockassembly is progressively increased as the depth of the hole is extendedand as further lengths of drill pipe are required to be added to thedrill string. FIGS. 6 and 9 show a condition of the shock assembly underpartial load intermediately of the conditions shown in FIGS. 1 and 5.

it has been found that a drill having a shock assembly 13 incorporatedtherein may be operated with shock absorbing characteristics under loadswithin a range from 0 to a maximum of approximately 200,000 lbs. It isunderstood that the number of ring elements 39 and spacers #il in theshock assembly may be selectively varied as desired.

It is understood that the sub unit may be located atany selected pointin the dril string; it is, however, preferably located as shownimmediately adjacent to the drill bit.

The squared portion 25 of the inner mandrel 22 has (FIG. 2) on each ofits iiats 57 a longitudinally extending slot 53 built up with a hardmetal alloy 59; and a complementary slot 6I on each of the flats 62 ofthe socket portion 26 of the outer mandrel 15 is similarly built up witha hard metal alloy 63. These areas of hardened metal are preferablylocated at those points of the socket 26 and shank 2S receiving thegreater components of force in the transmission of torque from the outermandrel to the inner mandrel.

What is claimed is:

l. A shock absorbing sub unit adapted to be coupled in the drill stringof a rotary earth-boring drill for absorbing vibrations created by thebit during drilling operations so as to prevent them from beingtransmitted to the drill string, comprising an inner driven open endedhollow mandrel connectible at its bottom end to the bit, an outeropen-ended hollow mandrel in coaxial surrounding relation to the innermandrel having a vertical slidable relation to the inner mandrel andconnectible at its top end to the drill string, shock absorbing meansslidably disposed between the inner and outer mandrels providingalternately -arranged compressible resilient members and pressuretransmitting members in sleeved relation to the inner mandrel andsupporting the outer mandrel upon the inner mandrel, a shoulder on theinner madrel defining a seat for one end of the shock absorbing means,an opposed shoulder internally of the outer mandrel seated upon theopposite end of the shock absorbing means, the interior of the innermandrel providing a iiuid passage to the bit, a pipe in the outermandrel providing a liuid passage from the drill string, a sleevesecured to the inner mandrel at one end having a slidable connection atits other with the pipe providing communication of the liuid passageswith one another and allowing slidable axial movement of the innermandrel relative to the pipe, means sealing the sleeve relative to theouter mandrel and the pipe against leakage of fluid around the pipe andsleeve to the shock absorbing means, and means independent of the shockabsorbing means forming a sole driving connection between the outer andinner mandrels for transmitting torque of the outer mandrel to the innermandrel.

2. A sub unit as defined in claim 1, wherein shoulder stop means isprovided internally of the outer mandrel above the shock absorbingmeans, and the Isleeve provides an end shoulder cooperable with the stopmeans to limit the extent of downward slidable movement of the innermandrel relative to the outer mandrel,

3. A shock absorbing sub unit comprising an inner mandrel connectable atits bottom to a drill bit, an outer mandrel sleeving the inner mandrelconnectable at its top to a drill string and having a vertical slidablerelationship with the inner mandrel, opposed longitudinally extendingwall portions of the mandrels defining an elongated cylindrical channelbetween the inner and outer mandrels in surrounding relation to theinner mandrel, shock absorbing means slidably disposed in the channelproviding alternately arranged compressible resilient ring members andpressure transmitting ring members in sleeved relation to the innermandrel and supporting the outer mandrel upon the inner mandrel, ashoulder on the inner mandrel defining a seat for one end of the shockabsorbing means, an opposed shoulder internally of the outer mandrelseated upon the opposite end of the shock absorbing means, and meansindependent of the shock absorbing means forming a sole drivingconnection between the inner and outer mandrels for transmitting torqueof the outer to the inner mandrel; wherein each resilient ring member isof polygonal coniiguration in cross section having an outermost diameteredge defining a circumferential corner and having an innermost diameteredge defining an annular corner respectively in contact with the opposedlongitudinally extending walls of the channel, and there being free flowspaces adjacent said corners relative to said walls.

4. A sub unit of the character described comprising an inner mandrelhaving a pin box at its bottom end adapted to be coupled with the pin ofa drill bit, an outer mandrel sleeving the inner mandrel having a pinadapted to be coupled with the pin box of a drill string, the innermandrel having a vertical slidable relationship with the outer mandrel,an elongated cylindrical channel defined between the inner and outermadrels in surroundig relation to the inner mandrel having an upperannular end wall defined by an internal shoulder of the outer mandreland lhaving a lower annular end wall defined by a shoulder of the innermandrel, a plurality of rigid spacer ring members and compressibleresilient ring members slidably sleeving the inner mandrel and soarranged that each resilient ring member is spaced from the other by aspacer ring member and wherein the lowermost and uppermost resilientring members respectively abut the lower and upper end walls of thechannel, a iiuid passage through the outer mandrel, a fiuid passagethrough the inner mandrel having a variable connection with the liuidpassage of the outer mandrel, means sealing the channel liuid tightagainst leakage from the fluid passages around the variable connectionto the spacer and resilient ring members, and a squared drive connectionbetween the outer and inner mandrels independent of the resilient ringand spacer members defining a sole means for transmitting rotary torqueof the outer mandrel -to the inner mandrel.

References Cited by the Examiner UNITED STATES PATENTS 2,113,651 4/1938Heaston 64-23 X 2,756,022 7/1956 Sturgeon 64-23 2,876,992 3/1959 Lindsay175-321 X 3,013,793 12/1961 Howell et al 175-321 X 3,225,566 12/1965Leathers 64-23 FRED C. MATTERN, JR., Primary Examiner.

HALL C. COE, Examiner.

1. A SHOCK ABSORBING SUB UNIT ADAPTED TO BE COUPLED IN THE DRILL STRINGOF A ROTARY EARTH-BORING DRILL FOR ABSORBING VIBRATIONS CREATED BY THEBIT DURING DRILLING OPERATIONS SO AS TO PREVENT THEM FROM BEINGTRANSMITTED TO THE DRILL STRING, COMPRISING AN INNER DRIVEN OPEN ENDEDHOLLOW MANDREL CONNECTIBLE AT ITS BOTTOM END TO THE BIT, AN OUTEROPEN-ENDED HOLLOW MANDREL IN COAXIAL SURROUNDING RELATION TO THE INNERMANDREL HAVING A VERTICAL SLIDABLE RELATION TO THE INNER MANDREL ANDCONNECTIBLE AT ITS TOP END TO THE DRILL STRING, SHOCK ABSORBING MEANSSLIDABLY DISPOSED BETWEEN THE INNER AND OUTER MANDRELS PROVIDINGALTERNATELY ARRANGED COMPRESSIBLE RESILIENT MEMBERS AND PRESSURETRANSMITTING MEMBERS IN SLEEVED RELATION TO THE INNER MANDREL ANDSUPPORTING THE OUTER MANDREL UPON THE INNER MANDREL, A SHOULDER ON THEINNER MADREL DEFINING A SEAT FOR ONE END OF THE SHOCK ABSORBING MEANS,AN OPPOSED SHOULDER INTERNALLY OF THE OUTER MANDREL SEATED UPON THEOPPOSITE END OF THE SHOCK ABSORBING MEANS, THE INTERIOR OF THE INNERMANDREL PROVIDING A FLUID PASSAGE TO THE BIT, A PIPE IN THE OUTERMANDREL PROVIDING A FLUID PASSAGE FROM THE DRILL STRING, A SLEEVESECURED TO THE INNER MANDREL AT ONE END HAVING A SLIDABLE CONNECTION ATITS OTHER WITH THE PIPE PROVIDING COMMUNICATION OF THE FLUID PASSAGESWITH ONE ANOTHER AND ALLOWING SLIDABLE AXIAL MOVEMENT OF THE INNERMANDREL RELATIVE TO THE PIPE, MEANS SEALING THE SLEEVE RELATIVE TO THEOUTER MANDREL AND THE PIPE AGAINST LEAKAGE OF FLUID AROUND THE PIPE ANDSLEEVE TO THE SHOCK ABSORBING MEANS, AND MEANS INDEPENDENT OF THE SHOCKABSORBING MEANS FORMING A SOLE DRIVING CONNECTION BETWEEN THE OUTER ANDINNER MANDRELS FOR TRANSMITTING TORQUE OF THE OUTER MANDREL TO THE INNERMANDREL.